This invention relates to damper mechanisms and more particularly to damper mechanisms in a counter shaft transmission.
Countershaft transmissions, often termed manual transmissions, have an input shaft, a countershaft, and an output shaft. The input shaft and countershaft are interconnected by meshing gears (head gear set). The countershaft and the output shaft are interconnected by a plurality of meshing gears (speed gears) that are selectively connectible to one of the shafts through synchronizer clutch arrangements. Thus a plurality of gear meshes are present between the input shaft and the output shaft.
The speed ratio between the input shaft and the output shaft is controlled by the meshing speed gears. The speed ratio between the input shaft and the output shaft is changed by interchanging the synchronizers that control the connection of the speed gears to their respective shafts. The head gear set and the active speed gear set have a lash condition. Under some operating conditions, the lash condition of the head gear set and the active speed gear set can reverse resulting in a noise or gear rattle caused by the lash reversal. This noise situation can occur during transient drive events such as throttle xe2x80x9ctip inxe2x80x9d and rapid clutch disengagement. As is well-known, the clutch is disengaged and re-engaged for each ratio interchange and during stopping and starting of the vehicle.
Some attempts have been made to quiet the gear disturbance. These include selecting specific bearing types, transmission architecture, and gear design to name a few. Each of these attempts result in increased drag on the shafts which is continuously present and therefore reduces the overall efficiency of the transmission.
It is an object of the present invention to provide an improved damper mechanism for use in a countershaft transmission.
In one aspect of the present invention, a selectively operable friction surface is disposed between two of the active shafts in a countershaft transmission. In another aspect of the present invention, an actuator is slidably positioned in one of the shafts to enforce activation of the friction surface. In yet another aspect of the present invention, the friction surface, when activated, is effective to retard any speed relation change between the input shaft and the output shaft of the transmission. In still another aspect of the present invention, the friction surface, when activated is effective to prevent a change in gear lash between meshing gears on the input shaft and the countershaft, and between active meshing gears on the countershaft and the output shaft.
The countershaft transmission has an input shaft that is coaxially aligned with and output shaft. A countershaft extends axially parallel with the input and output shafts. A head gear set having a member drivingly connected with each of the input shaft and the countershaft cause these shafts to rotate in opposite directions. A plurality of speed gear sets disposed on the countershaft and the output shaft are selectively actuated to establish respective speed ratios between these shafts. Each of the speed gear sets has one gear member continuously rotatable with one shaft and the other gear member is selectively connectable with the other shaft by a synchronizer clutch. A selectively actuatable clutch is disposed between an engine crankshaft and the transmission input shaft.
A selectively engageable friction member is positioned between the input shaft and the output shaft. A linear actuator, slidably disposed in the input shaft, is energized to cause a frictional drive relation between the input shaft and the output shaft which presents the speed relation therebetween from changing rapidly. Since the speed relation between the input shaft and output shaft is unchanging, the speed relation between the countershaft and the other shafts is also unchanging. The linear actuator is operated by an electromagnetic mechanism, in one embodiment, when the system is subjected to a transient condition that would be effective to reverse the gear lash between the mating gears. Such transient conditions are caused by rapid clutch disengagement or throttle release (throttle tip out). Since rapid changes in rotational acceleration are known to cause gear separation noise, other control mechanisms such as rotational acceleration mechanisms, which can be mechanical, hydraulic or electrical, can also be employed to effect the actuation of the friction member. However, since the conventional electronic control unit for the vehicle has all of the input signals necessary to control the actuation of the friction member, the electrically actuated piston is deemed to be preferred.